Process for producing pellets with cement

ABSTRACT

A process for producing pellets, which comprises blending 98 to 60% by weight of iron ores and 2 to 40% by weight of a mixture, comprising 95 to 15% by weight of cement and 5 to 85% by weight of iron containing powders smaller than 100 meshes and with addition of 9 to 20% by weight of water on the basis of the mixture.

AU 115, EX

PROCESS FOR PRODUCING PELLETS WITH CEMENT Inventors: Shunsaku Shimada;Tadahiro Inazumi, both of Tokai, Japan Nippon Steel Corporation, Tokyo,Japan Nov. 30, 1973 Assignee:

Filed:

Appl. No; 420,568,

Published under the Trial Vo1untary Protest Program on January 28, 1975as document no. B 420,568.

[1.8. CI. 75/3; 106/89; 106/104 Int. Cl. C2IB l/24; C04B 7/22 Field ofSearch 75/3-5;

References Cited UNITED STATES PATENTS 7/1914 Mathesuis ..7s/3 3/1916Dery ..75/3

[ Dec. 9, 1975 1,315,315 9/1919 Lammerhirt 75/3 2,363,371 11/1944 Vignos75/3 2,887,392 5/1959 Lolley 106/104 X 2,910,372 10/1959 Ruskin 106/893,235,371 2/1966 VaIin et aI, 75/3 3,374,085 3/1968 Stone 75/3 3,490,8951/1970 Svensson 75/3 FOREIGN PATENTS OR APPLICATIONS Japan 106/89Primary Examiner-Allen B. Curtis Attorney, Agent, or Firm-Toren, McGeadyand Stanger tg'ning powderssmaller than 100 meshes and with addition oto 0% by weight of water on the basis of the mixture.

2 Claims, 3 Drawing Figures U.S. Patent Dec. 9, 1975 Sheet 1 of 23,925,069

FIGZ

US. Patent Dec. 9, 1975 Sheet 2 of2 3,925,069

SHRINKAGE m 01 C; o

PRESSURE DROP (mm .aq.)

800 900 I000 n00 |200 |300 I400 TEMPERATURE (c) PROCESS FOR PRODUCINGPELLETS WITH CEMENT The process of the present invention relates to aprocess for producing pellets.

As well-known, sintered ores are mostly used for the blast furnacematerials. However, troubles of public nuisance are brought about bythese sintered ores due to the dusts or exhaust gas, generated duringthe production. Therefore, pellets, and particularly cold pellets aredrawing attention. But the conventional cold pellets are inferior in hotproperties. That is, the strength is decreased at 700 to 1300C. Duringthe operation of a blast furnace, they are degradaded in the furnace andrepeat the swelling and shrinkage, so that the gas permeability isimpaired and the furnace condition is made unstable.

Until now, there has been proposed for example a pelletizing process,such as Grangcold pelletizing process, which is disclosed in US. Pat.No. 3,490,895. According to this process, iron ores are mixed withcement and pelletized. The thus obtained pellets are covered with fineores and hardened for about a week. After the fine ores are separated byscreening, the pellets are hardened, with a long time taken. The featureis to cover the pellets with fine ores after pelletization so that thepellets may be prevented from mutual attachment and deformation.

Though this process enables the production on an industrial scale, thestages of work are complicated and necessitates a large amount ofconstruction cost and running expenses since the stage of covering withfine ores, the stage of hardening pellets, the stage of separating fineores and others are required. And yet, the hot properties of the productduring the reduction are not considerably improved as compared with theconventional. Accordingly, there is a limitation for use in the presentoperation of a blast furnace.

The present invention is to provide a process for producing a coldpellet in a simple stage of work and besides, with excellence in coldstrength and of course, hot strength.

The gist is that cement, ferruginous powders (containing metallic iron)and iron ores are mixed and pelletized in an ordinary pelletizingprocess. Because of blending ferruginous powders into cement, thehardening of cement, and accordingly, of pellets can be achieved in ashort time by the oxidizing exothermic reaction of Fe, contained in theferruginous powders. And moreover, the expansion and contraction can berestrained by ferruginous powders. Thus, the process can be simplifiedby such like and besides, the hot.

properties may be remarkably improved.

For the cement to be used according to the present invention, there maybe used ordinary commercial cement, for example, Portland cement,pozzolan cement, slag cement, aluminate cement. A favourable effect canbe obtained with use of aluminate cement.

The ferruginous powder to be used in the present invention will do if itis a pulverized material, having metallic Fe contained, such as cuttingscrap of iron, atomized iron powder, reduced iron powder, ferruginousscale or the like.

Any iron ore used for producing an ordinary pellet may be used in thepresent invention.

When cement, ferruginous containing metallic iron powders and iron oresare mixed and this mixture is added with water to be pelletizedaccording to the present invention, the oxidizing exothermic reaction ofFe, contained in the ferruginous powders, is employed to accelerate thehardening of cement and to restrain the expansion and contraction duringthe time of hardening, whereby the process can be simplified and the hotproperties of the produced pellet during the reduction may be improved.In order to achieve this object, the mixing ratio of the above mentionedthree components is limited in the present invention as follows:

1. Mixing ratio of ferruginous powder to cement ferruginous powder 5 topreferably 20 to 60% by weight 2. Mixing ratio of cement and ferruginouspowder to iron ore cement and ferruginous powder 2 to 40%, preferably 10to 30% by weight If the ratio of ferruginous powder to cement is below5% by weight, the oxidizing exothermic reaction'o'f Fe becomesinsufficient, and it becomes difficult to restrain the swelling andshrinkage of the pellet during the reduction at the time of hardening,so that the hot properties of the pellet cannot be improved. While, ifthe ratio is above 85% by weight, the quantity of cement becomes shortand the bonding power is insufficient, so that the satisfactory pelletcannot be obtained.

Further, the finer the ferruginous powder is, the better it is toimprove the pelletizing property and the reactivity of Fe. It isnecessary to use the particles under meshes (by Tailor). It ispreferable that the particles are under 300 meshes. If the particles areover 100 meshes, the pelletization becomes difficult by the differenceof specific gravity from the iron ore.

The reason for that the mixing ratio of cement and ferruginous powdersto iron ores is limited to 2 to 40% by weight in the present inventionas above mentioned, is that the bonding powder is insufficient in caseof less than 2%, while the slag component becomes more in case of above40%, so that the grade is too low to be used in practice as the ironsource for a blast furnace material.

The grain size of iron ore may be the grain size of an ordinary pelletmaterial in consideration of the pelletizing property. But in order toprevent agglomeration during the hardening of pellets, it is preferablethat there exist 2 to 10% by weight of ores, having the grain size of0.25-to 1 mm.

An appropriate quantity (9 to 20% by weight) of water is added in orderto pelletize the mixture of the three components, mixed as abovementioned.

The present invention shall be explained referringto the drawings,wherein;

FIG. 1 shows a process according to the conventional method;

FIG. 2 shows an example of the process according to the presentinvention; and

FIG. 3 is a graph, showing the comparison of the hot properties of apellet during the reduction between the conventional method and theprocess of the present invention.

In FIG. 1, 11 is a hopper for fine iron ores; 12, a hopper for cement;13, a mixer; 14, a pelletizer; 15, a hopper for fine iron ores; 16, ahopper for preliminary hardening; and 17, a screen for fine iron ores.

FIG. 2 shows an example of the process according to the presentinvention and 1 shows a hopper for cement; 2, a hopper for ferruginouspowders; 3, a mixer; 4, a hopper for iron ores; 5, a mixer; 6, apelletizer; 7, a yard for pellets; 7', an indoor yard; and 8, a blastfurnace.

The cement and the ferruginous powders, charged out respectively fromthe hopper l for cement and the hopper 2 for ferruginous powders, aremixed in a mixer 3 and then configurated with the fine iron ores,charged out from a hopper 4 for iron ores. They are mixed in a mixer 5and fed into a pelletizer 6 to be pelletized.

The mixer 3 is used for mixing before the cement and the ferruginouspowders are blended with the iron ores. But it may be omitted accordingto circumstances. If it is omitted, the three components, namely cement,ferruginous powders and iron ores, are mixed in the mixer 5. However, inorder to improve the effect of the present invention, it is better touse the mixer 3. The pellets, pelletized in the pelletizer 6, arehardened as they are, ordinarily in the yard 7, but may be hardened inthe indoor yard 7' in order to prevent the influence from such as rains.Then, the pellets are fed in a reducing fumace.

The process, shown in FIG. 1, is characterized by the omission of apreliminary hardening stage, necessary for the Grangcold pelletizingprocess, and also the op- I eration of covering with fine iron ores.That is to say,

according to the conventional method cement has a low velocity ofhardening and remains in a plastic condition for a long time withoutincrease of the strength. And besides, the swelling and shrinkage duringthe hardening are great, so that a pressing power is produced andtogether with gravity, makes the pelletized pellets agglomerated ordeformed. Therefore, it is necessary to perform a preliminary hardeningwith fine iron ores inserted among the pellets. On the contrary,according to the present invention the hardening velocity of cement isincreased by the oxidizing exothennic reaction of ferruginous powdersand the strength is relatively increased early. When the pellets areleft in a stacking, they will not be crushed. The swelling and shrinkageof cement are restrained by the ferruginous powders during the stacking,so that the external factors of agglomeration or deformation can bereduced. According to the present invention the agglomeration ordeformation of the pellets can be effectively prevented by making coarseparticles above 0.25 mm present in the fine iron ores at the rate of 2to 10% by weight.

The hot properties of the pellets according to the conventional methodsand the present invention are compared in FIG. 3. (A) shows a standardWayara pellet (oxidized and baked pellet); (B), a pellet according toExample 1 of the present invention; and (C), a pellet according to theGrangcold pelletizing process.

The conventional cold pellet (C) is inferior in its hot properties, andparticularly in the loaded softening property to the standard pellet (A)as shown in FIG. 3. On the contrary, the pellet (B) of the presentinvention is remarkably improved in its hot properties as comv paredwith the pellet (C) of the Grangcold pelletizing process, so that it canbe used in a large amount for the operation of a blast furnace.

Further, for the hot properties, swelling becomes a problem when thepellet is used in a blast fumace. There may be at least about 10% ofswelling in the conventional method. However, the swelling can berestrained to about 1% according to the present invention.

Thus, it is the effect of the ferruginous powders that the hotproperties, namely the loaded softening property and swelling can berestrained. That is to say, the

hot strength of the conventional pellet becomes lowest at the Wustitestage and changes to recover when metallic Fe begins to be generated,while according to the present invention ferruginous powders arepreviously blended, so that the generation of the nucleus of metallic Fecan be helped and the strength (loaded softening property) of the pelletcan be improved. The swelling of the pellet in the blast furnace is dueto the fibrous metallic iron, generated during the reducing process.According to the present invention ferruginous powders are previouslyblended for the existence of the Fe nucleus. The fibrous metallic iron,which begins to be generated, is adhered with each other and coagulated.Thus, the swelling may be prevented.

The embodiment examples of the present invention shall be explained inthe following.

Example 1:

Blending of raw materials;

Cutting scrap 5% size '200 mesh Alumina cement(commercial) 10% 50%+0.25mm 6% average size 0.19 mm Iron sand Sinter dust, collected byelectric collector 35% 200 mesh Water 12% of the above mixture Hardeningtime: one month Crushing strength: 143.2 Kg/pellet Swelling 1% Note:Measuring method of swelling Volumetric change at 900C for 3 hours in areducing atmosphere, having 30% of CO and of N.

Blending of raw materials:

Reducing iron powders l0% size 200 mesh Portland cement (commercial) 15%Kamaishi concentrates 50% +0.25 mm 7% Lamco fine ores 25% -200 meshWater 14% of the above mixture Hardening time one month Crushingstrength 2 205 Kglpellet Swelling 1.1%

powder, reduced iron powder and ferruginous scale.

* w s s

1. A PROCESS FOR PRODUCING PELLETS, WHICH COMPRISES BLENDING 98 TO 60%BY WEIGHT OF IRON ORES AND 2 TO 40% BY WEIGHT OF A MIXTURE COMPRISING 95TO 15% BY WEIGHT OF CEMENT AND 5 TO 85% BY WEIGHT OF IRON CONTAININGPOWDERS SMALLER THAN 100 MESHES WITH ADDITION OF 9 TO 20% BY WEIGHT OFWATER ON THE BASIS OF THE MIXTURE.
 2. A process according to claim 1, inwhich the iron containing powder is one or more selected from the groupconsisting of cutting scrap of iron, atomized iron powder, reduced ironpowder and ferruginous scale.